This invention relates to surface-treating agents for copper and copper alloy which are used in manufacturing of printed circuit.
Recently, printed circuit has become increasingly important as packaging parts while steadily and step by step overcoming technical obstacles produced by development of smaller, lighter and more multifunctional electronic instruments. With the progress of automation of the package of electronic instruments, lines of the print circuit have been finer, the holes smaller in diameter, and the system more multilayered, and technical improvement of the formation of so-called high density circuit is more and more desired.
In association with the development of high density printed circuit, steps for applying various platings such as electroless copper plating subsequent to various processings of the copper-plated laminate have increased.
Thus, so-called soft etching step for (1) removal of the anticorrosive and the oxide film remaining on the surface of copper foil of the copper-plated laminate (2) roughing of the copper surface for activating the copper surface and improving adherence of the plating, (3) removal of the flaws formed on the processed surface, etc. plays an important role.
Furthermore, due to the development of finer patterns of printed circuit, mechanical or pamis polishing heretofore employed has become technically difficult, and substitution of the polishing with chemical cleaning is desired.
Heretofore, ammonium persulfate or sodium persulfate is used as the soft etching agent. Ammonium persulfate, however, is defective in that copper ammonium complex is formed during neutralization due to co-existence of ammonium ions in the effluent, and copper in the wastewater cannot be removed.
Sodium persulfate also needs various measures for improving performance which is inferior to that of ammonium persulfate. In addition, there are such disadvantages as short life, frequent bathings and high cost for manufacturing in the etching solution using ammonium persulfate or sodium persulfate.
Application of soft etching with an acid aqueous solution of hydrogen peroxide has the heretofore been attempted in order to overcome such disadvantages. However, the prior-art acid aqueous solutions of hydrogen peroxide are encountered with problems as follows:
(1) Two-step treatment involving soaking aftertreatment with diluted sulfuric acid or diluted hydrochloric acid is required due to formation of oxide film on the copper surface after soft etching.
(2) Rate of dissolving copper is apt to be influenced by the change of hydrogen peroxide concentration in the etching solution so that finish of the copper surface is not uniform.
(3) Adherence of the plating is inferior as compared with soft etching with ammonium persulfate.
Polishing with an acid hydrogen-peroxide system has been proposed as a chemical polishing substitution for the mechanical polishing as mentioned above. In general, however, this process needs a two-step treatment in which oxide film is first formed with hydrogen peroxide and sulfuric acid and then the oxide film is removed with a diluted aqueous solution of an acid. Improved one-step chemical polishing methods by addition of phosphoric acid and an amine are proposed in Japanese Patent Publication Nos. 32339/1978 and 32340/1978. These methods are not adaptable to use in the high-density printed circuit because of such disadvantages that they are not economical due to high hydrogen-peroxide concentration of 5%-60% and even the addition of phosphoric acid and an amine cannot lead to complete removal of the oxide film.